Heretofore, when printed circuit boards were temporarily fitted or mounted with so-called SMD such as chip resistors, chip capacitors, SOT's, flat-pack IC's, etc. having no lead-wire, use of an adhesive which is curable by both ultraviolet light and heat has been known. An adhesive of this sort is applied onto a printed circuit board by the screen printing method, a method using a dispenser apparatus, a method using a transfer pin, etc., and, after cautiously placing SMD on the printed circuit board, an ultraviolet light is irradiated to cure the adhesive. In this case, even the adhesive portions that have not been irradiated with an ultraviolet light, such as the adhesive underlying the SMD, can also be completely cured either by heat which is subsidiarily generated at the time of irradiation of an ultraviolet light or by combined use of a curing furnace separately installed.
In such a prior art technique, ultraviolet light-curable adhesives which are endowed with heat curing properties by the addition of a heat polymerization initiator such as organic peroxides have been used.
However, adhesives which have hitherto been known have a number of defects in storage stability, gel time, coating properties, heat curing speed, adhesion strength, etc. That is, if the heat curing speed is increased, not only does the storage stability become poor, but also the viscosity of the adhesive remarkably rises which adversely affects the coating properties. On the other hand, if the storage stability is improved, although the coating properties are improved, the heat curing speed becomes so slow that the adhesion strength and gel time can no longer be sufficient. Therefore, none of the conventional adhesives can satisfy all of the storage stability, coating properties heat curing speed, gel time, and adhesion strength simultaneously.